The present invention relates to a flame detecting apparatus for detecting the flame of a fire and the like using a sensor.
Conventionally, a flame detecting apparatus for detecting flames has been known in which the ultraviolet rays (with wavelength of 180 nm to 260 nm) from the flame are sensed by an ultraviolet sensor (for example, ultraviolet detection tube), and the occurence of flame is detected when the number of discharge pulses for a predetermined period output from the ultraviolet sensor exceeds a specified level.
FIG. 19 shows a block diagram of this kind of flame detecting apparatus. Referring to FIG. 19 , this flame detecting apparatus is provided with an ultraviolet sensor 71, a sensitivity adjustment unit 72 for applying voltage to the ultraviolet sensor 71, a signal processing unit for judging whether or not the number of discharge pulses for a predetermined period exceeds a specified level, and an output unit 75 for outputting a message that there is fire or the like when the number of discharge pulses for a predetermined period exceeds a specified level. These elements of the apparatus are mounted on one circuit board forming a unit.
Incidentally, the condition of the flames of a fire is changed by a combustion state, environmental influences, etc. For example, strong flame may occur for a short period of time, or weak flame may occur for a long period of time.
In the conventional flame detecting apparatus mentioned above, the counting period can be set to an arbitrary value, however, this conventional flame detecting apparatus encounters a problem in that when the counting period is set to be short, strong flames can be detected at an early stage, but weak flames occurring for a long time fail to be detected.
While, when the counting period is set to be long, weak flames occurring for a long time can be detected, but strong flames cannot be detected in the early stages. Moreover, when the counting period is set to be long, influences from noise, etc. are easily received, and the frequency of erroneous detection of flame is higher.
Furthermore, in the conventional flame detecting apparatus, the sensitivity rank of the ultraviolet sensor 71, which is used in the apparatus, was adapted to be tested with a specific testing device in the assembly and manufacture of this flame detecting apparatus as a unit on the circuit board, and based on the test results, it was necessary to perform an evaluation of the quality, sensitivity adjustment, functional check and so on. Therefore, there is another problem in the conventional apparatus in that the testing process using the specific testing device, which is separate from the flame detecting apparatus, causes the assembly or manufacturing process to be too complicated, and makes it impossible to accurately adjust, inspect or test the whole apparatus in the assembly factory.
In addition, after the assembled flame detecting apparatus has been installed in a predetermined installation location to be used as a fire alarm, etc., it needs general periodic inspection to test whether or not the apparatus is operating normally. This periodic inspection or testing has conventionally been conducted by, for example, removing the apparatus from the installation location, and either returning it to the assembly factory for inspection or testing, or by bringing a separate testing device to the installation location and testing the apparatus with a testing device similar to that used during assembly. Based on the results of this inspection, the sensitivity was adjusted and the functions were checked, thus completing the periodic inspection and testing of the flame detecting apparatus.
Therefore, in performing periodic inspection or testing of the flame detecting apparatus at the installation site, or when the apparatus malfunctions, it is necessary to remove the flame detecting apparatus from the site, and to inspect or test it with the specific testing device, which makes inspection or testing of the apparatus too difficult.